Unusual polymerization behavior of water-soluble fullerenols in laser desorption ionization time-of-flight mass spectrometry

Laser desorption ionization time-of-flight mass spectrometry has been used to study the water-soluble multi-hydroxyl C-60 derivatives - fullerenols. The mass spectra exhibit unusual polymerization behavior of fullerenols. (C) 1997 by John Wiley & Sons, Ltd.

An ESR study on (OH)-O-center dot-radical scavenging activity of water-soluble fullerenols

Water-soluble polyhydroxylated fullerene derivatives (fullerenol) were synthesized, and their scavenging ability for (OH)-O-.-radical was studied by the combination of ESR spectroscopy and spin-trapping technique with phenyl-t-butyl-nitrone. It was found that fullerenols showed an excellent efficiency in eliminating (OH)-O-. free radicals generated by UV photolysis of H2O2. At an applied fullerenol concentration of 0, 3 mg/mL in the final solution, a radical scavenging efficiency of approximate 95% was achieved, revealing the potential use of these compounds as novel potent free radical scavengers in biological systems.

Gas permeability in polyimides from oxydianiline and isomeric thiaphthalic dianhydride or 1,4-bis(dicarboxyphenoxy) benzene dianhydride

The gas permeability and permselectivity properties were investigated of polyimides, prepared from 3,3',4,4'- and 2,2',3,3'-thiaphthalic dianhydride (p-TDPA and m-TDPA, respectively), or 1,4-bis(3,4-dicarboxyphenoxy)- and 1,4-bis(2,3-dicarboxyphenoxy) benzene dianhydride (p-HQDPA and m-HQDPA, respectively), and 4,4-oxydianiline. The polyimides prepared from meta-dianhydrides, which have lower chain-segment packing density, possess higher permeability and lower permselectivity than those prepared from para-dianhydrides. Copyright (C) 1996 Elsevier Science Ltd.

Effects of molecular structure on the permeability and permselectivity of aromatic polyimides

Permeability coefficients of H-2, O-2, and N2 were measured under 10 atm at the temperature from ambient temperature up to 150 degrees C in a series of structurally different aromatic homo- and copolyimides, which were prepared from 4,4'-oxydianiline (ODA) or 4,4'-methylene dianiline (MDA) with various aromatic dianhydrides. The study shows that the molecular structure of the polyimides strongly influences gas permeability and permselectivity. As a result, the permeability coefficients of the polyimide membranes for each gas vary by over two orders of magnitude. In general, among the polyimide membranes studied, the increase in permeability of polymers is accompanied by the decrease in permselectivity, and the MDA-based polyimide membranes have higher permeability than ODA-based ones. Among the polyimides prepared from bridged dianhydrides, the permeability coefficients to H-2, O-2, and N-2 are progressively increased in the order BPDA < BTDA < ODPA similar to TDPA < DSDA ( SiDA < 6FDA, while H-2/N-2 and O-2/N-2 permselectivity coefficients are progressively decreased in the same order. The copolyimide membranes, which were prepared from 3,3',4,4' biphenyltetracarboxylic dianhydride (BPDA), bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride (SiDA), and ODA, have favorable gas separation properties and are useful for H-2/N-2 separation applications. (C) 1996 John Wiley & Sons, Inc.

NMR Spectra of polyimides: Interpretation and local chain motion study

Three kinds of high-performance polyimides 1 (poly(ketone-imide) PKI), 2 (poly(ether-imide) PEI) and 3 (poly(oxy-imide) POI) were studied using nuclear magnetic resonance (NMR). The NMR spectra of the polyimides were assigned according to the comprehensive consideration of the substitution effect of different substituting groups, viz. distortionless enhancement by polarization transfer (DEPT), no nuclear Overhauser effect (NNE), analysis of relaxation time, and two-dimensional correlated spectroscopy (COSY) techniques. The structural units of these three polyimides were determined. Carbon-13 and proton relaxation times for PEI and PKI were interpreted in terms of segmental motion characterized by the sharp cutoff model of Jones and Stockmayer (JS model) and anisotropic group rotation such as phenyl group rotation and methyl group rotation. Correlation times for the main-chain motion are in the tens of picosecond range which indicates the high flexibility of polyimide chains. Correlation times for phenyl group and methyl group rotations are more than 1 order of magnitude lower and approximately 1 order of magnitude higher than that of the main chain, respectively.

Comparative study on polyimides from 3,3'- and 4,4'-linked diphthalic anhydride

1,4-Bis(2,3-dicarboxyphenoxy)benzene dianhydride, 1,4-bis (3,4-dicarboxyphenoxy)benzene dianhydride, bis(2,3-dicarboxyphenoxy) sulfide dianhydride, bis (3,4-dicarboxyphenoxy)sulfide dianhydride, and 2,3,3',4'-tetracarboxy diphenyl sulfide dianhydride were synthesized from 3-chlorophthalic anhydride and 4-chlorophthalic anhydride. Bis(2,3-dicarboxyphenyl)sulfone and bis(3,4-dicarboxyphenyl) sulfone were obtained by the oxidation of the corresponding bis(dicarboxyphenyl)sulfide by hydrogen peroxide. The polyimides from the dianhydrides mentioned above and 4,4'-oxydianiline were prepared. The properties, such as dynamic mechanical behavior, thermooxidative stability, stress-strain behavior, chemical resistance, and permeability to some gases have been in investigated for the isomeric polyimides. (C) 1996 John Wiley & Sons, Inc.

GAS PERMEABILITIES AND PERMSELECTIVITY OF PHOTOCHEMICALLY CROSS-LINKED POLYIMIDES

Photosensitive polyimide BTDA-3MPDA was modified by UV irradiation. The structure of UV-irradiated polyimides was investigated by FTIR and gel fraction measurements. The results showed that longer UV exposure time resulted in a higher extent of crosslinking. The gas permeabilities of hydrogen, oxygen and nitrogen through UV-irradiated polyimides were characterized in a temperature range from 30 degrees C to 90 degrees C. Photocrosslinking resulted in a sharp decline in gas permeability for hydrogen, oxygen, and nitrogen through polyimide in the initial stage of photocrosslinking. Then, as the crosslinked benzophenone percentage amounted to 28-38% for hydrogen, 17-31% for oxygen and 3-28% for nitrogen, the gas permeabilities showed another sharp decline. Gas permselectivity increased significantly with the progress of photocrosslinking, and it can be adjusted in a wide range by controlling the extent of crosslinking. Arrhenius plots of gas permeability for hydrogen and oxygen through UV-irradiated polyimides are straight lines; for nitrogen, however, change in the slope of the straight line is observed and activation energies for hydrogen and oxygen permeation show abrupt increases when crosslinked benzophenone percentage amounts to about 30%. UV-irradiated polyimides with simultaneous high gas permeability and permselectivity make them ideal candidate materials for gas separation. (C) 1995 John Wiley & Sons, Inc.

BETA-RELAXATION IN POLYIMIDES

A series of polyimides with different structures have been synthesized and studied by dynamic mechanical analysis. The results obtained indicate that the beta relaxation in polyimides is related to the rotation of rigid segment(s) of p-phenylene and imide groups around 'hinges' such as -O-, -CH2- and so on in diamines. It is noticed that two kinds of polyimides both with [GRAPHICS] imide groups have verv weak beta relaxation below the glass transition temperature. This phenomenon is due to the fact that the configuration of chains with the above imide groups hinders the rotation of the rigid segments in the chains.

C-13 NMR CHARACTERIZATION OF SOLUBLE POLYANILINE

A high-resolution C-13 n.m.r. spectrum of soluble polyaniline in DMF-d7 solution was recorded. The assignment for the various resonance peaks in the spectrum was tentatively performed and the chain structure of polyaniline was analysed. It has been shown that the main chain of pristine state polyaniline is composed of alternating benzoid-quinoid and successive benzoid-quinoid sequences with the former being present in greater concentration. The sequence distribution is random. In addition to the benzoid-type and quinoid-type structures, there is a small amount of other structural units in the main chain.

WATER-SOLUBLE AND AMPHIPHILIC POLYMERS .11. GRAFT-POLYMERIZATION OF ACRYLIC-ACID ON POLY(VINYL ALCOHOL)

The graft polymerization of acrylic acid(AA) on poly(vinyl alcohol) (PVAL) has been investigated by using either potassium persulfate (KPS) or ceric ammonium nitrate(CAN) as an initiator. In the case of KPS initiation, the formation of the graft polymer always lags behind the homopolymer formation. The graft polymer is separated by acetone, and the increase of reaction temperature favors the homopolymer formation at the early stage. In the case of CAN initiation, graft polymers with a high PAA content can hardly be obtained when the polymerization is performed under nitrogen and at < 0.06 mol/L HNO3 concentration. It has been found that incorporation of a small amount of oxygen in a protective nitrogen gas accelerates markedly the graft polymerization, and that the resulting graft polymers can not be separated by acetone precipitation technique in most cases. The Dalian nitrogen(containing 0.7% oxygen) is a good protective gas for CAN-initiated PVAL-AA graft polymerization.

THERMAL-ANALYSIS OF POLYARYLENE ETHER SULFONES AND POLYIMIDES

Some results on the thermal analysis of polyimides and polyaryl ether sulfones, some reactions and the purity determination of the monomers, and the thermal stability and kinetic analysis of the thermo-oxidative degradation of these polymers are described.

WATER-SOLUBLE AND AMPHIPHILIC POLYMERS .6. A STUDY ON THE SURFACE-COMPOSITION OF CAST FILMS OF PST/PMAA AND PEO-PST-PEO BLOCK POLYMERS BY XPS

Thin films of PSt/PMAA and PEO-PSt-PEO block polymers were deposited on a polystyrene substrate by solution adsorption (with or without solvent treatment), and the film surfaces were characterized by means of XPS. Direct solvent - casting of PEO-PSt-PEO from benzene solutions resulted in PSt-rich surfaces, whereas PMAA richer surfaces were obtained for PSt/PMAA films cast from DMF solutions. Moreover, solvent treatment after casting had profound effect on the film surface composition. Treatment with water markedly increased the surface concentration of polar PEO segments. In the case of PSt-PMAA block polymers, the PSt content on the surface increased in the order of water < ethanol < cyclohexane < petroleum ether, the last-named giving films with almost pure PSt surface. It is well worth noticing that the bulk composition had little to do with the surface composition for both PSt/PMAA and PEO-PSt-PEO block polymers within the composition range investigated when subsequent solvent treatment was applied.

WATER-SOLUBLE AND AMPHIPHILIC POLYMERS .7. SYNTHESIS AND CHARACTERIZATION OF A NOVEL COMB-TYPE AMPHIPHILIC POLYMER PAMC16S

A novel comb-like amphiphilic polymer, poly (2-acrylamidohexadecylsulfonic acid) (PAMC16S), was synthesized by free radical polymerization of the corresponding amphiphilic monomer in 1,4-dioxane-water mixed solvents. Depending on the ratio of water/dioxane in the solvent, the reaction proceeded by either precipitation polymerization or micellar polymerization. The molecular weight of the polymer obtained under similar conditions decreased and subsequently increased with the increase of water content in the mixed solvent. The polyion nature of PAMC16S was confirmed by viscosity data of ethanolic solutions. In addition, the polymer was characterized by solubility, IR, TG and wide angle X-ray diffraction methods.